Electron structure of heavy atoms - Structure of matter Flashcards
What are the two things that broadly determine the electron structure of atoms with many electrons?
The electron structure of atoms with many electrons is mainly determined by two rules:
1) System of particles is stable at a minimum total energy.
2) Only one electron exists in each individual quantum state of the atom.
How is the state of each electron in a heacy atom determined?
Similarly to the hydrogen atom, the state of each electron in a heavy atom is determined by four quantum numbers.
What is the charge of the electrons in the atom and what is shielding?
Each electron moves in a central force field of a nucleus with the charge Ze (where Z is the atomic number) and it is also shielded by the presence of other electrons less distanced from the nucleus.
What do electrons with the same principal quantum number have in common?
All the electrons with an identical principal quantam number are roughly equally distanced from the nucleus and thus, they interact with the same intensity of the field and possess roughly the same energies.
We say that the shell, denoted by the letters K, L, M etc, is occupied.
What is the highest possible number of electrons in each shell?
Since (2ℓ+1) values of the magnetic quantum number correspond to each orbital quantum number ℓ and spin number has two possible values, the highest number of electrons present in each shell is 2n2.
However the electron energy also depends on the orbital quantum number, it rises with increaing ℓ, and its dependance on ℓ also increases with increaing number of electrons in the atom.
What does a ‘closed’ shell imply?
The shell (given by n) or subshell ( ℓ), which is completly occupied by electrons, is called closed.
The closed subshell s ( ℓ=0) contains two electrons, the closed subshell p ( ℓ=1) six electrons, the subshell d ( ℓ=2) ten electrons etc.
Total orbital and spin angular moment of electrons in a closed subshell equals zero and the distribution of their effective charge is completly symmetrical.
Explain periodicity.
Periodicity of physical and chemical proterties of elements follows form subsequent filling of electron shells.
In the case of heave atoms, we meet the situation that higher shells are filled before omplet filling of the prevous one (with respect to the possible number of electrons given by the value 2n2).
This fact results from the request for a minimum total energy of the system with respect to its stability.
The order of filling of shells in heavy atoms is as follows:
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 6d.
E.g.
Since the energy of state 3d exceeds that of state 4s, the level 4s is filled formerly.
However states s and p in the previous shell must be completly filled up before filling the states in shell with higher n.
Explain Hund’s rule.
Besides Pauli’s principle, Hund’s rule plays an important rule in filling the shells with electrons:
If possible, electrons in shells generally remain unpaired,
I.e. they possess parallel spins.
This results fro mutual respulsion of electrons.
Electrons with parallel spin are more separated in space as compared with paired electrons and this arrangement possesses a lower energy and thus a higher stability.
